Laminate damping base material, and damping structure with stack of this base material

ABSTRACT

A damping structure which dispenses of the connection of a resistor used for a conventional damping structure and undergoes diverse molding processings with a simpler structure, and a laminate damping base material constituting such a damping structure. A laminate damping base material made of a piezoelectric ceramic material or piezoelectric polymer material and a conductive fiber-reinforced plastic (FRP) composition is prepared. One to a plurality of this base material are stacked to constitute a first damping structure. A second damping structure is constituted by stacking at least a layer of piezoelectric polymer film or piezoelectric ceramic thin film between a multilayer laminate that is a laminate of conductive laminate FRP base materials.

TECHNICAL FIELD

The present invention relates to a laminate damping base material, and adamping structure with stack of the base material.

BACKGROUND ARTS

Fiber-reinforced plastic (FRP) has been used in general industrialstructures and as structural materials for a wide range of fields suchas aerospace and energy, due to its lightweight, high strength and highrigidity features.

While various characteristics are required for structural frameworks, ithas recently become very important to develop a technology forsuppressing or lowering vibrations among the above-describedcharacteristics in terms of improvement of positional accuracy ofstructures and improvement in reliability of incorporated equipment.

However, the oscillation-damping characteristics of FRP is generallylow, which is considerably inferior to that of metallic structures.Therefore, the present inventor developed a damping structure A (FabricEngineering, Vol. 51, No. 3 (1998)) in which piezoelectric ceramics 5and 6 are adhered to both sides of the outside of an FRP laminatedstructure 4 and a resistor 7 is connected between the respectivepiezoelectric ceramics 5 and 6 as shown in FIG. 3, in order to improvethe oscillation-damping characteristics of FRP.

The presumed principle of damping using the piezoelectric ceramics isbased on that, when an external force is applied to the piezoelectricceramics, electric charge is generated by a piezoelectric effect, andelectric energy is dissipated as Joule heat by causing the electriccharge to pass through a resistor connected between the piezoelectricceramics.

However, since it is necessary to connect a resistor to the outside ofthe above-described damping structure, there are disadvantages in termsof structure when such a damping structure is applied to practicalapplications provided with various molding processes.

The present invention was developed in view of the above-describedproblems and shortcomings, and it is therefore an object to provide adamping structure with simpler structure, which does not requireconnection of any resistor used for prior art damping structures and canbe provided with various molding processes, and a damping base materialfor lamination which is a member of the above damping structure.

SUMMARY OF THE PRESENT INVENTION

A damping structure for lamination according to the present inventioncomprises a piezoelectric ceramics material or a piezoelectric polymermaterial and a fiber-reinforced plastic (FRP) compound havingconductivity.

Also, grains consisting of at least one type of ceramics materialsselected from lithium niobate (LiNbO₃), barium titanate (BaTiO₃), leadtitanate (PbTiO₃), lead zirconate titanate (PZT), and lead metaniobate(PbNb₂O₆) are preferably used as the above-described piezoelectricceramics material.

In addition, fine grains obtained by cutting a film made of afluorine-based polymer material are preferably used as theabove-described piezoelectric polymer materials. In detail, one type ofresin material selected from monopolymers of polyvinylidene fluoride,co-polymers of vinylidene fluoride and trifluoroethylene, andco-polymers of vinylidene fluoride and tetrafluoroethylene may bepreferably used as the above-described piezoelectric polymer material.

Further, a reinforcing material made of carbon fibers and a matrix madeof plastic may be preferably used as the above-described FRP compositionhaving conductivity.

At least one type of reinforcing material selected from glass fibers,aramid fibers, silicon carbide (SiC) fibers, and boron fibers; at leastone type of conductive material selected from metallic powder, graphiteand carbon black; and a matrix made of plastic may be preferably used asthe above-described FRP composition having conductivity.

A first damping structure according to the present invention isconstructed by laminating one or a plurality of the above-describeddamping base material. Also, the damping structure is constructed bysequentially laminating the damping base materials so that the fabricdirection of fabrics composing one damping base material does notoverlap with the fabric direction of fabrics composing another dampingbase material directly laminated on the one damping base material,thereby obtaining a lamination structure in which anisotropy of rigiditythat damping base materials originally hold is mitigated, wherein themechanical properties of the damping structure can be made excellent.

In addition, the first damping structure according to the presentinvention is favorable since the oscillation-damping characteristics canbe synergistically improved by adhering piezoelectric ceramics to bothsides of the outside of the damping structure and connecting thepiezoelectric ceramics via an electric resistor in addition to theabove-described construction.

In addition, the first damping structure according to the presentinvention is favorable since the oscillation-damping characteristics canbe synergistically improved by laminating at least one layer ofviscoelastic polymer film between the damping structures in addition tothe above-described construction. In detail, a polyorefin-based film maybe preferably used as the viscoelastic polymer film.

Also, a second damping structure according to the present invention isfeatured in that at least one layer of piezoelectric polymer film orpiezoelectric ceramics thin film is laminated between multi-layeredlaminated structures in which a plurality of FRP base materials havingconductivity are laminated.

A fluorine-based polymer is preferable as the above-describedpiezoelectric polymers. In detail, at least one type of polymer selectedfrom monopolymers of polyvinylidene fluoride, co-polymers of vinylidenefluoride and trifluoroethylene, and co-polymers of vinylidene fluorideand tetrafluoroethylene may be preferably used.

Also, at least one type of ceramics materials selected from lithiumniobate (LiNbO₃), barium titanate (BaTiO₃), lead titanate (PbTiO₃), leadzirconate titanate (PZT), and lead metaniobate (PbNb₂O₆) may bepreferably used as the above-described piezoelectric ceramics material.

Also, a reinforcing material made of carbon fibers and a matrix made ofplastic may be preferably used as the above-described FRP base materialhaving conductivity.

At least one type of reinforcing material selected from glass fibers,aramid fibers, silicon carbide (SiC) fibers, and boron fibers; at leastone type of conductive material selected from metallic powder, graphiteand carbon black; and a matrix made of plastic may be preferably used asthe above-described FRP base material having conductivity.

In addition, the second damping structure according to the presentinvention is favorable since the oscillation-damping characteristics canbe synergistically improved by adhering piezoelectric ceramics to bothsides of the outside of the damping structure and connecting thepiezoelectric ceramics via an electric resistor in addition to theabove-described construction.

In addition, the second damping structure according to the presentinvention is favorable since the oscillation-damping characteristics canbe synergistically improved by laminating at least one layer ofviscoelastic polymer film between the damping structures in addition tothe above-described construction. In detail, a polyorefin-based film maybe preferably used as the viscoelastic polymer film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of the first damping structure of the presentinvention.

FIG. 2 shows an embodiment of the second damping structure of thepresent invention.

FIG. 3 shows an example of a prior art damping structure.

FIG. 4 shows a relationship between a resonance mode of the firstdamping structure and loss factor thereof.

FIG. 5 shows a relationship between a resonance mode of the seconddamping structure and loss factor thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, a description is given of a laminate damping base materialand a damping structure with stack of the base material accordinglythereto according to the present invention.

First, there are two types of damping structure according to the presentinvention, the first type (hereinafter called a “first dampingstructure”) in which a piezoelectric ceramics material or apiezoelectric polymer (hereinafter called a “piezoelectric material”)exists in a granular, powdery granular or fine granular form, and thesecond type (hereinafter called a “second damping structure”) in which apiezoelectric material exists in a film-like or thin membrane-like form.Also, the first damping structure is constructed by laminating alaminate damping base material according to the present invention as oneunit. The following description is given with items classified asfollows: a laminate damping base material being a construction member ofthe first damping structure, the first damping structure, and the seconddamping structure.

[Laminate Damping Base Material]

A laminate damping base material (hereinafter called a “damping basematerial”) according to the present invention comprises a piezoelectricmaterial and a fiber-reinforced plastic (FRP) composition havingconductivity. In the present invention, it is preferable that thedamping base material is molded so as to have a fixed shape and a fixedthickness. And the damping base material is used as a member of thefirst damping structure according to the present invention constructedby laminating a plurality of damping base materials. Also, the dampingbase material according to the present invention may comprise a singlelayer construction in which a piezoelectric material is dispersed withthe above-described FRP, or may comprise a two-layer constructionconsisting of an FRP composition and a piezoelectric material layer byspraying and adhering the piezoelectric material onto the outer surfaceof the FRP composition. Hereinafter, a description is given of acomposition material of the damping base material.

The piezoelectric material used for the damping base material has a roleof converting vibration energy to electric energy when an external forceis applied to the damping base material. A material havingpiezoelectricity, that is, a material that is instantaneously distortedwhen an external force is applied and generates electric charge ispreferable as the piezoelectric material. In particular, a piezoelectricceramics material or a piezoelectric polymer material may be preferablyused.

Lithium niobate (LiNbO₃), barium titanate (BaTiO₃), lead titanate(PbTiO₃), lead zirconate titanate (PZT), and lead metaniobate (PbNb₂O₆)may be listed as preferable piezoelectric ceramics materials. Thesecompositions may be preferably used independently or in a combination ofa plurality thereof.

Since it is necessary to spray and adhere the above-describedpiezoelectric ceramics material onto the outer surface of an FRPcomposition having conductivity or to disperse the same in theabove-described FRP composition, the above-described piezoelectricceramics material is preferably used in the form of grains. Also, thereis no special limitation in grain size, grain shape and blendingquantity of the piezoelectric ceramics material where the piezoelectricceramics materials are used as grains. That is, the grain size, grainshape and blending quantity may be adequately designed so that theproductivity and piezoelectricity of the damping base material can beoptimized.

Meanwhile, a fluorine-based polymer material may be listed as apreferable piezoelectric polymer material. In detail, monopolymers ofpolyvinylidene fluoride, co-polymers of vinylidene fluoride andtrifluoroethylene, and co-polymers of vinylidene fluoride andtetrafluoroethylene may be listed. These may be preferably usedindependently or in a combination of a plurality thereof.

In addition, generally, since a polymer material used for the presentinvention takes on piezoelectricity by employing a method (this methodis called “poling”) for returning to a room temperature after causingpolarization (residual polarization) by applying a high electric fieldto the extended material resin at a high temperature including and lessthan a melting point, the polymer material is necessarily used in theform of a film. Therefore, it is preferable that the film is cut in theform of fine grains in order to bring about desired piezoelectricity byspraying and adhering the film to the outer surface of FRP compositionhaving conductivity or dispersing the film in the above-described FRPcomposition.

The FRP composition used in the damping base material has rigidity as adamping base material, allows electric charge to pass through, which isgenerated when an external force is applied to the above-describedpiezoelectric material, and at the same time has a role of convertingelectric energy to Joule heat as a resistor of electric charge. In thepresent invention, it is preferable in terms of cost that theconstructing material of the FRP composition is made different, in thecases where a fabric material having conductivity (hereinafter called a“conductive fabric material”) is used and a fabric material not havingany conductivity (hereinafter called a “non-conductive fabric material”)is used.

Hereinafter, a description is given of the FRP composition in the casesof the conductive fabric material and non-conductive fabric material.

Where the conductive fabric material is used, by using a reinforcementmaterial composed of a conductive fabric material and a matrix made ofplastic as indispensable components, it is possible to compose an FRPcomposition having desired conductivity in the present invention. Here,carbon fibers are preferably used as the conductive fabric material.

Further, as the plastic provided as the matrix, it is possible to use apublicly known thermo-setting resin or thermoplastic resin, which areused as fiber-reinforcing plastic. For example, unsaturated polyesterresin, epoxy resin, phenol resin, melamine resin, silicone resin, etc.,may be preferably used as the thermo-setting resin. On the other hand,polyamide resin, acetar resin, polycarbonate resin, vinyl chlorideresin, ABS resin, engineering plastic resin, polyethylene resin,polypropyrene resin, polyestyrene resin, methacryl resin, fluorineresin, saturated polyester resin, AS resin, etc., may be preferably usedas the thermoplastic resin.

Where the non-conductive fabric material is used, by using a reinforcingmaterial made of anon-conductive fabric material, a matrix made ofplastic, and a conductive material as indispensable components, it ispossible to compose a FRP composition having desired conductivity in thepresent invention. Herein, glass fibers, aramid fibers, silicon carbide(SiC) fibers, and boron fibers are preferably used as the non-conductivefabric material. Also, these may be preferably used independently or ina combination of a plurality thereof.

Also, as plastic, it is possible to use a publicly known thermo-settingresin or thermoplastic resin, which are used as fiber-reinforcingplastic. For example, unsaturated polyester resin, epoxy resin, phenolresin, melamine resin, silicone resin, etc., may be preferably used asthe thermo-setting resin. On the other hand, polyamide resin, acetarresin, polycarbonate resin, vinyl chloride resin, ABS resin, engineeringplastic resin, polyethylene resin, polypropyrene resin, polyestyreneresin, methacryl resin, fluorine resin, saturated polyester resin, ASresin, etc., may be preferably used as the thermoplastic resin.

In addition, metallic powder, graphite and carbon black may bepreferably used as the conductive material. Further, these may bepreferably used independently or in a combination of a pluralitythereof. The blending ratio of a conductive material to the damping basematerial may be adequately designed to an optimal quantity in responseto the conductive properties when being made into the damping basematerial, wherein there is no special limitation.

As described above, the damping base material according to the presentinvention may be made into a single-layer construction in which apiezoelectric material is dispersed with respect to the above-describedFRP composition or may be made into a double-layered constructionconsisting of an FRP composition layer and a piezoelectric materiallayer by spraying and adhering the piezoelectric material onto the outersurface of the FRP composition. Therefore, in the present invention,there is no special limitation in that the construction is made into onelayer or a double layer.

However, since the dispersion of a piezoelectric material with respectto the FRP composition generally differs according to whether the fibermaterial contained in the FRP composition is short or long, it ispreferable to adequately design the layer construction of the dampingbase material in response to the shape of the fabric material whenproducing the damping base material.

In detail, a single layer construction is preferable where short fibersare used, and a double-layer construction is preferable where longfibers are used.

Next, a description is given of a method for producing the damping basematerial. First, where either of a conductive fiber or non-conductivefiber is used, these fibers may be preferably used in the processed formof woven fabric (hereinafter called a “fabric base material”). There isno special limitation in the form of woven fabric. However, generally,plain woven cloth, satin cloth, roving cloth, and filament wound clothmay be preferably used independently or in a combination thereof. Also,where it is desired that a high-strength damping base material beconstructed, the above-described fabric being intensively pulled in onedirection may preferably used.

For example, the damping base material of a mono-layered structure isproduced by dispersing a piezoelectric material in a melted resin ofplastic and then immersing the above-described fabric base materialcomposed of carbon fibers therein and hardening the melted resin. Also,the damping base material of a double-layered structure is produced byimmersing the above-described fabric base material made of carbon fibersin a plastic melted resin and then spraying and adhering a piezoelectricmaterial to the outer surface of the melted resin of plastic.

In addition, where a thermo-setting resin is used as a resin, it ispossible to produce a semi-hardened damping base material (so called“prepreg”). Since such a damping base material has some viscosity, it ispreferable in terms of production because, where the first dampingstructure according to the present invention is produced by overlappinga plurality of damping base materials, it is possible to easily laminaterespective damping base materials by heating and compressing operations.

The above-described damping base material of a mono-layered structure isconstructed with the piezoelectric material disposed in an FRPcomposition having conductivity. Therefore, where an external force isapplied to the damping base material, the following energy conversion isbrought about. First, when an external force (a mechanical vibrationenergy) is applied to a damping base material, the vibration energy isconverted to electric energy by a piezoelectric effect of thepiezoelectric material existing in the entirety of the damping basematerial, and electric charge is generated in a wide range of thedamping base material. And, the electric charge thus generated flows inthe entire damping base material by a conductive action of theconductive substance, and a majority of electric energy is converted toJoule heat in the entire damping base material by actions of a resistorof the conductive substance. And, the converted Joule heat is dissipatedoutside of the damping base material, consequently energy applied to theinside of the damping base material is reduced.

Also, the above-described damping base material of a double-layeredstructure is constructed by the piezoelectric material and FRPcomposition having conductivity respectively forming separate layers.Therefore, when an external force is applied to a damping base material,the following energy conversion is brought about. First, when anexternal force (a mechanical vibration energy) is applied to the dampingbase material, the vibration energy is converted to electric energy in anarrow area of the damping base material by a piezoelectric effect of apiezoelectric material concentrated in and existing in the piezoelectricmaterial layer, thereby generating electric charge. And, the electriccharge thus generated flows in the entirety of the damping base materialby a conductive action of the conductive substance contained in theentire FRP composition, and at the same time, a majority of electricenergy is converted to Joule heat in a wide range of the damping basematerial by actions of a resistor of the conductive substance. And, theconverted Joule heat is dissipated outside the damping base material,consequently the energy applied to the inside of the damping basematerial is reduced.

[First Damping Structure]

The first damping structure according to the present invention isproduced by laminating one or a plurality of the above-described dampingbase materials and processed to be molded as a multi-layered laminatestructure by carrying out compression and heating. The compressing andheating conditions of the damping base material are not speciallylimited. The compressing and heating conditions may be adequatelyestablished to optimal conditions in response to a damping base materialused.

Further, in the present invention, where a damping structure isconstructed by laminating a plurality of damping base materials upwardone upon another, it is preferable that such a laminate structure isemployed, by which anisotropy of rigidities which the respective dampingbase materials inherently hold can be mitigated. Hereinafter, adescription is given below of this point, taking an instance of adamping structure in which damping base materials of a mono-layeredstructure are laminated.

As shown in FIG. 1, the damping structure 1 is constructed in such amanner that, where the fabric direction of fabrics composing the firstdamping base material 11 is regarded as reference (0°) and the fabricdirection of fabrics composing the second damping base material 12 is+45°, the second damping base material 12 is laminated above the firstdamping base material 11, hereinafter, the third damping base material13 is laminated above the second damping base material in the fabricdirection of −45°, and further the fourth damping base material 14 islaminated above the third damping base material in the fabric directionof 90°, wherein one or a plurality of sets, each of which is composed offour base materials laminated in the directions of [0°/+45°/−45°/90°],are laminated one upon another (In the present specification, thelaminate structure is called a “Quasi-equal rectangular laminateconstruction”).

Also, a damping structure in which one or a plurality of laminatestructures having two damping base materials laminated at [0°/90°] islaminated may be listed as another example (in the presentspecification, the laminate construction is called a “Cross-shapedlaminate construction”).

That is, it is preferable that a laminate construction in which thefabric directions of the respective damping base materials arecompletely different from each other is composed as a set, and one or aplurality of sets of the laminate construction are laminated to producea damping structure. By employing such a laminate construction, theanisotropy in rigidities that the damping base materials inherently holdcan be abated in various directions, wherein it is possible to reducethe anisotropy in rigidity when being fabricated as a damping structure,and the damping structure is able to have further favorable mechanicalproperties.

Next, a description is given of the presumed damping principle of thefirst damping structure. The first damping structure is constructed bylaminating one or a plurality of damping base materials having theabove-described energy converting action. Therefore, when an externalforce is applied to the first damping structure 1, vibration energy istransmitted to the entirety of individual damping base materials whichare components, and the vibration energy is converted to electric energy(generation of electric charge) by a piezoelectric effect of apiezoelectric material dispersed in and existing in the individualdamping base materials. Subsequently, the generated electric charge ismostly converted to Joule heat by resistance when it flows in theindividual damping base materials, and the Joule heat is dissipated.That is, since the vibration energy remaining after the above-describedprocess is considerably reduced from the initial vibration energy, it ispossible to quickly attenuate the vibrations of the damping structure.

The first damping structure according to the present invention isfeatured in that it does not require any external resistor used in priorart damping structures and is constructed by laminating one or aplurality of layers of a damping base material constructed by dispersinga conductive material acting as an internal resistor and a piezoelectricmaterial for converting mechanical energy to electric energy. The firstdamping structure succeeds in providing damping characteristics with avery simple construction as a structure.

Also, the construction of the first damping structure is as describedabove. However, by adequately combining technical elements used in theprior art damping structure with the first damping structure, it ispossible to synergistically improve the damping characteristics. Forexample, such a construction may be employed, in which piezoelectricceramics are adhered to both sides of the outside of the first dampingstructure, respectively, and these piezoelectric ceramics are connectedto each other via electric resistors. Or, such a construction may alsobe employed, in which at least one layer of viscoelastic polymer film(for example, polyorefin-based film) is laminated between the firstdamping structures. The damping principle of the latter dampingstructure in which a viscoelastic polymer film is inserted is based onvibration energy being converted to thermal energy by slip deformationof the film and being dissipated.

As has been described above, the first damping structure according tothe present invention has excellent damping control characteristics as amulti-layered laminate structure of FRP. Therefore, since such astructure has excellent vibration attenuation performance andnoise-proofing and noise-silencing performance in addition to beinglightweight and having high strength, it can be used in various fieldsas a structure. For example, it can be used as an excellent dampingmaterial in a wide range of fields such as robot arms, windmillmaterials for wind power generation, automobiles, vehicles, vessels,sports materials (golf shafts, tennis rackets), etc.

In addition, the first damping structure can be used as excellentsoundproofing and sound insulation materials in civil engineering andbuilding fields and in various types of machines and electriccomponents.

[Second Damping Structure]

The second damping structure according to the present invention isconstructed by laminating at least one layer of piezoelectric film orpiezoelectric thin film (hereinafter called a “piezoelectric film (thinfilm)”) between FRP multi-layered structures constructed by laminating aplurality of laminate FRP base materials having conductivity.Hereinafter, a description is given of respective composing materials.

First, the piezoelectric film (thin film) has a role of convertingvibration energy to electric energy when an external force is applied tothe second damping structure. A material showing piezoelectricity, thatis, a film or a thin film composed of a material that is instantaneouslydistorted when an external force is applied and generates electriccharge is preferable as the piezoelectric film (thin film). Inparticular, a thin film of piezoelectric ceramics or a film of apiezoelectric polymer may be preferably used.

Those used in the above-described laminate damping base material may beused as a piezoelectric ceramics material composing the thin film ofpiezoelectric ceramics and a piezoelectric polymer material composing afilm of piezoelectric polymer. In addition, the thickness of the thinfilm or film may be adequately designed so as to obtain an optimalpiezoelectric property, wherein there is no special limitation.

A laminate FRP base material having conductivity has rigidity as adamping base material, and the same laminate FRP base material has arole of allowing electric charge, which is generated when an externalforce is applied to the above-described piezoelectric film (thin film),to pass through and convert electric energy to Joule heat as a resistorof electric charge. Also, the material composing the laminate FRP basematerial may be similar to the FRP composition used for theabove-described laminate damping base material. FRP base materialsavailable on the market may be used as they are. In detail, if alaminate base material (prepreg) composed of carbon fibers andthermo-setting resin and available on the market is used, it is notnecessary to newly produce an FRP base material. Further, since it ispossible to easily carry out laminate molding of the base materials, thesecond damping structure according to the present invention can beeasily produced.

The second damping structure is constructed by laminating at least onelayer of piezoelectric film (thin film) between a multilayered structureconstructed by laminating a plurality of laminate FRP base materialshaving conductivity. First, on the basis of the same reason as describedin the first damping structure, it is preferable that the FRP basematerials are laminated so that the anisotropy of rigidities which theindividual FRP base materials inherently hold is mitigated. For example,as shown in FIG. 2, a plurality of FRP base materials 21 are laminatedwith quasi-equal rectangularity, and next, the above-describedpiezoelectric film (thin film) 3 is inserted and adhered between the FRPbase materials 21 and 21, wherein it is possible to produce the seconddamping structure 2. There is no special limitation in the shape,dimension, position and quantity of the piezoelectric films (thin films)to be inserted, and these factors may be adequately designed so as toobtain the optimal piezoelectric characteristics. In addition, withrespect to a method for adhering the piezoelectric film (thin film) andFRP base materials, a publicly known adhesive agent may be used unlesssufficient adhering strength is obtained with a normal heatpressure-fitting operation.

Next, a description is given of the presumed damping principle of thesecond damping structure. When an external force is applied to thesecond damping structure, vibration energy is first generated, and thevibration energy is instantaneously converted to electric energy(electric charge is generated) by a piezoelectric effect of thepiezoelectric film (thin film) as soon as the vibration energy reachesthe piezoelectric film (thin film). Next, a majority of the vibrationenergy is converted to Joule heat by resistance applied to the generatedelectric charge flowing in the FRP, and the Joule heat is dissipated.That is, since the vibration energy remaining after the above-describedprocess is considerably reduced from the initial vibration energy, it ispossible to quickly attenuate the vibrations of the damping structure.

The second damping structure according to the present invention isfeatured in that it does not require any external resistor used in priorart damping structures and it contains uniformly a dispersed conductivematerial as an internal resistor and it further comprises inside thedamping structure a piezoelectric body in the form of a film (thin film)which converts mechanical energy to electric energy. Therefore, thesecond damping structure succeeds in achieving damping characteristicswith a very simple structure as a structure.

The construction of the second damping structure is as described above.However, by adequately combining technical elements used in the priorart damping structure with the second damping structure, it is possibleto synergistically improve the damping characteristics. For example,such a construction may be employed, in which piezoelectric ceramics areadhered to both sides of the outside of the second damping structure,respectively, and these piezoelectric ceramics are connected to eachother via electric resistors. Or, such a construction may also beemployed, in which at least one layer of viscoelastic polymer film islaminated between the second damping structures. The damping principleof the latter damping structure in which a viscoelastic polymer film isinserted is based on vibration energy being converted to thermal energyby slip deformation of the film and being dissipated.

As has been described above, the second damping structure according tothe present invention has excellent damping control characteristics as amulti-layered laminate structure of FRP. Therefore, since such structurehas excellent vibration attenuation performance and noise-proofing andnoise-silencing performance in addition to being lightweight and havinghigh strength, it can be used in various fields as a structure. Forexample, it can be used as an excellent damping material in wide rangeof fields such as robot arms, windmill materials for wind powergeneration, automobiles, vehicles, vessels, sports materials (golfshafts, tennis rackets), etc.

In addition, the second damping structure can be used as a structure incivil engineering and building fields and in various types of machinesand electric components as excellent soundproofing and sound insulationmaterials.

Hereinafter, a further detailed description is given of the presentinvention on the basis of embodiments. However, the present invention isnot limited to the embodiments.

[Composing Materials]

One-direction carbon/epoxy prepreg (Brand name: Torayca T800H/#2500,Toray Industries, Inc.) was used as laminate FRP. Polyvinylidenefluoride (PVDF) (Brand name: Kureha KF polymer: Kureha ChemicalsIndustries, Ltd.) was used as a piezoelectric polymer.

Lead zirconate titanate (PZT) was used as piezoelectric ceramics. Leadzirconate titanate (PZT) (Brand name: C-82, Fuji Ceramics Co., Ltd.) wasused as a raw material of a piezoelectric ceramics sheet. Thepiezoelectric ceramics sheet whose dimensions are 10 mm×15 mm×0.28 mmwas used.

[Embodiment 1]

By spraying PZT grains, whose mean grain size is 6.5 μm, onto a singleside of the outside of a laminate FRP having dimensions of 90 mm longand 15 mm wide at a spraying quantity of 9.26 grams per square meter, alaminate damping base material having PZT grains adhered and fixed onthe surface of a laminate FRP was prepared. In this connection, sincethe above-described laminate FRP is a semi-hardened type prepreg and hasadequate viscosity, the PZT grains could be easily adhered and fixed onthe surface of the laminate FRP. Next, the laminate damping basematerial was laminated in a cross-like laminate construction of[0°/90°/90°/0°] and was subjected to autoclave processing for threehours under a temperature of 130° C. at 5 bars, thereby having preparedthe first damping structure in which four laminate damping basematerials are laminated.

[Comparative Example 1]

A damping structure was prepared, which is the same as the Embodiment 1excepting that PZT grains are not dispersed and fixed on a singlesurface of the outside of the laminate FRP.

[Evaluation of Dynamic Characteristics]

With respect to the above-described two types of structures, acantilever beam type vibration test in which one end of the structure isfixed while the other free end thereof is vibrated was carried out, andloss factor were calculated with respect to the first through fourthresonance modes. The results are as shown in FIG. 4.

[Embodiment 2]

A laminate FRP whose dimensions are 70 mm long and 15 mm wide islaminated in a cross-shaped laminate construction of [0°/90°/90°/0°],and a piezoelectric polymer film (15 mm wide ×10 mm long) was insertedbetween 90° and 90°. The same laminate FRP was subjected to autoclaveprocessing for three hours under a temperature of 110° C. at 5 bars,thereby having prepared the second damping structure. The piezoelectricpolymer film was inserted in the single side end of the laminatestructure.

[Embodiment 3]

A piezoelectric ceramics sheet was adhered to both sides of the outsideat the single side end of the damping structure as prepared inEmbodiment 2, and these piezoelectric ceramics sheets were connected toeach other via an electric resistor. Also, the polarization direction ofthe respective piezoelectric ceramics sheets was oriented toward theoutside direction.

[Comparative Example 2]

A damping structure which is the same as the Embodiment 2 excepting thatthe piezoelectric polymer film is not inserted was prepared.

[Comparative Example 3]

The piezoelectric ceramics sheet used in Embodiment 3 is adhered to bothsides of the outside of the single side end of the damping structureprepared in Comparative example 2, and the piezoelectric ceramics sheetsare connected to each other via an electric resistor.

[Evaluation of Dynamic Characteristics]

A cantilever beam type vibration test was carried out with respect tothe above-described four types of structures. Loss factor werecalculated with respect to the first through fourth resonance modes. Theresults are as shown in FIG. 5.

[Result]

As shown in FIG. 4, Embodiment 1 showed a greater loss factor than thatof the Comparative example 1 in all of the first through fourthresonance modes. It was thereby confirmed that the first dampingstructure according to the present invention shows higher dampingcharacteristics than the FRP structure (Comparative example 1) in whichprepreg including conventional carbon fibers is laminated.

Also, as shown in FIG. 5, Embodiments 2 and 3 showed greater loss factorthan those of Comparative examples 2 and 3 in all of the first throughfourth resonance modes. On the basis of the above-described results, itwas confirmed that both means (Embodiment 2) for inserting apiezoelectric polymer film in the FRP multilayered structure and means(Embodiment 3) for adhering piezoelectric ceramics sheets to both sidesof the outside of a single side end of a damping structure via anelectric resistor in addition to the above-described means according tothe Embodiment 2 show high damping characteristics.

Further, in all the resonance modes, Embodiment 3 showed a greater lossfactor than Embodiment 2. Thus it is confirmed that, by adhering apiezoelectric ceramics sheet to both sides of the outside of the singleside end of a damping structure and causing an electric resistor tointervene therebetween, a synergistic effect of the dampingcharacteristics is brought about.

INDUSTRIAL APPLICABILITY

As has been described above, since the first damping structure accordingto the present invention is constructed by laminating one or a pluralityof damping base materials according to the present invention, in which apiezoelectric material is dispersed on an FRP composition havingconductivity, the first damping structure has excellent dampingperformance and noise-proofing and noise-silencing performance inaddition to being lightweight and having high strength.

In addition, the second damping structure according to the presentinvention is constructed so that a piezoelectric material is insertedand laminated in the form of a sheet or a thin film between FRP laminatestructures having conductivity, and consequently the second dampingstructure has excellent damping performance and noise-proofing andnoise-silencing performance in addition to being lightweight and havinghigh strength.

1. A laminate damping base material comprising a grain piezoelectricceramics material or a grain piezoelectric polymer material sprayed andadhered onto an outer surface of a fiber-reinforced plastic (FRP)composition having conductivity.
 2. The laminate damping base materialas set forth in claim 1, wherein the piezoelectric ceramics material isa grain composed of at least one type of ceramics materials selectedfrom lithium niobate (LiNbO₃), barium titanate (BaTiO₃), lead titanate(PbTiO₃), lead zirconate titanate (PZT), and lead metaniobate (PbNb₂O₆).3. The laminate damping base material as set forth in claim 1, whereinthe piezoelectric polymer material is a grain obtained by cutting a filmmade of a fluorine-based polymer material.
 4. The laminate damping basematerial as set forth in claim 3, wherein the fluorine-based polymermaterial is at least one type of resin materials selected frommonopolymers of polyvinylidene fluoride, co-polymers of vinylidenefluoride and trifluoroethylene, and co-polymer of vinylidene fluorideand tetrafluoroethylene.
 5. The laminate damping base material as setforth in any one of claim 1 through claim 4, wherein the FRP compositionhaving conductivity includes a reinforcing material made of carbonfibers and a matrix made of plastic.
 6. The laminate damping basematerial as set forth in any one of claim 1 through claim 4, wherein theFRP composition having conductivity includes at least one type ofreinforcing materials selected from glass fibers, aramid fibers, siliconcarbide (SiC) fibers, and boron fibers; at least one type of conductivematerials selected from metallic powder, graphite and carbon black; anda matrix made of plastic.
 7. A damping structure having a laminatedamping base material described in claim 1 laminated in a plurality oflayers.
 8. The damping structure as set forth in claim 7, wherein saidlaminate damping base materials are laminated sequentially so that thedirection of fibers composing one laminate damping base material and thedirection of fibers composing another laminate damping base materialdirectly laminated on said one laminate damping base material do notoverlap each other, and anisotropy in rigidities that the laminatedamping base materials hold is mitigated.
 9. The damping structurehaving piezoelectric ceramics adhered to both sides of the outside ofthe damping structure described in claim 8, wherein said piezoelectricceramics are connected via an electric resistor.
 10. The dampingstructure having at least one layer of viscoelastic polymer filmlaminated between the damping structures described in claim
 9. 11. Thedamping structure as set forth in claim 10, wherein the viscoelasticpolymer film is a polyolefin-based film.